The present invention relates generally to operating a hydraulic device and in particular to a hydraulic circuit connected to a stripper for sealing off and holding wellbore fluids in a well, and a method of controlling the sealing of tubing associated therewith.
Coiled tubing injectors are used to grip and advance coiled tubing into a well via a wellhead. Many coiled tubing injectors utilize a stripper to seal off and hold wellbore fluids in the well. The stripper, also called a stripper/packer, lubricator, or stuffing box, is typically positioned above the wellhead and utilizes one or more hydraulic actuated cylinders to press stripper elements (or pack-off elements) against the coiled tubing while the tubing is being inserted into or removed from the well, thereby sealing the wellhead and preventing the release of wellbore fluids from the well. The cylinder or cylinders in the stripper are controlled using a stripper hydraulic circuit connected thereto.
Several potential problems arise during the operation of a typical stripper hydraulic circuit. For example, if the diameter of the tubing increases during the operation of a typical stripper hydraulic circuit, there may be an unsafe pressure increase in the circuit. Also, many stripper hydraulic circuits require a human operator to move near the stripper during operation to adjust the sealing pressure on the tubing, thus increasing the risk of harm to the operator. Further, if there is a loss of pressure to the stripper hydraulic circuit, the seal against the tubing will be broken and wellbore fluids will be released from the wellhead, creating both a safety and environmental hazard and possibly damaging any equipment in the vicinity of the wellhead.
Current solutions to a loss of pressure in the stripper hydraulic circuit include using a shut-off valve to isolate the stripper hydraulic circuit after the loss of pressure, or connecting a check valve upstream of the stripper hydraulic circuit to hold pressure in the stripper hydraulic circuit. Although these solutions prevent a complete loss of pressure to the stripper hydraulic circuit, they do not provide an easy way for the human operator to resume control of the stripper hydraulic circuit after the pressure has been restored. In addition, neither of these solutions enables the sealing pressure on the tubing to be increased in the event of a loss in pressure to the hydraulic circuit or other unforeseen emergency.
Therefore, what is needed is a hydraulic circuit for controlling a stripper that overcomes these problems.